In a communication system, the control channels between cells interfere with each other, which disrupts user services. Therefore, to solve the cross interference of control channels between cells, two cells may use orthogonal transmission of downlink control channels to transmit control channels of the user. For example, in cell 1, the downlink control channel (PDCCH) is transmitted within an f1 frequency range. Therefore, for a user of a new communication system, the downlink control channel (PDCCH) falls within the f1 frequency range, and the downlink shared channel (PDSCH) falls within the entire downlink bandwidth frequency range. In cell 2, the PDCCH is transmitted within an f2 frequency range. Therefore, for the user of the new communication system, the downlink control channel (PDCCH) falls within the f2 frequency range, and the downlink shared channel (PDSCH) falls within the entire downlink bandwidth frequency range. There may be no overlap or an overlap part between the f1 frequency range and the f2 frequency range. In this way, the frequency of the PDCCH of cell 1 is completely or partly orthogonal to the frequency of the PDCCH of cell 2, which prevents neighboring cell interference to the control channel and improves the receiving performance of the control channel.
Besides, in the new communication system, a multi-carrier transmission technology may provide wider bandwidth, or a single carrier is divided into multiple carriers so that inter-cell interference coordination is accomplished through inter-carrier coordination. The user in the new communication system can access multiple carrier units simultaneously.
In the prior art, the new communication system is not backward-compatible in the case of orthogonal transmission of the downlink control channel or multi-carrier transmission. Consequently, the existing communication system that does not support orthogonal transmission or multi-carrier transmission is unable to work normally.